The present invention relates to a distributor of the type which is employed in an electric ignition system of a multi-cylinder internal combustion engine and, more particularly, to a distributor for an internal combustion engine which is improved in both reliability and durability.
In general, a distributor for internal combustion engines comprises a housing, a shaft inserted in the housing and mounted to rotate synchronously with the crankshaft of the engine, a rotor head attached to an end of the shaft to distribute electric current, and a cap for closing the housing and having electrodes for inputting electric current to the rotor head and for outputting a distribution electric current. Such a distributor also may accommodate a signal detector and other electrical devices inside the housing in order to reduce the overall size of an internal combustion engine and accommodate other devices in available spaces within the distributor rather than on the internal combustion engine. Japanese Patent Publication No. 45-26527/1970 discloses one example of this type of distributor. It is necessary, in order to accommodate various kinds of electrical devices inside the distributor housing, to give special consideration to the waterproofness, heat resistance, etc. of the distributor housing.
One of the problems concerning waterproofness relates to the fact that it is difficult to provide both for waterproofness and ease of assembly of the distributor.
The signal detector installed inside the housing of a distributor is provided with a connector inserted in an opening formed in the side wall of the housing so as to project outside of the housing. The connector is fixed to the housing by screws through an annular rubber gasket fitted on the connector. However, this structure needs a large number of components and therefore provides for difficulties in assembly of the distributor.
The above-mentioned structure for enhancing waterproofness gives rise to a problem that dissipation of heat generated inside the housing is likely to be obstructed. In the distributor in which an ignition coil is accommodated inside the housing, the heat resistance of the ignition coil must be enhanced.
However, the improvement in heat resistance that is attained simply by enhancing the heat resistance of the constituent material is limited and it is therefore necessary to improve the heat resistance by enhancing both suppression of heat generation and dissipation of heat.
In the distributor in which an ignition coil is accommodated, a core of the ignition coil and the housing are in contact with each other through a seat; however, the area for heat transfer is relatively small and therefore dissipation of heat through conduction at the seat does not satisfactorily take place. Further, there is a problem of generation of heat from the ignition coil.
In order to increase the efficiency of dissipation of heat from electrical devices, a heat dissipating plate has been provided between the signal detector and the housing and is fastened to the housing together with the signal detector by means of fastening screws.
In this prior arrangement, one of the fastening screws is disposed in such a manner as to be inserted into the annular core, while the other screw is disposed outside the core. Accordingly, a short-circuit is formed by a part of the housing and the heat dissipating plate in such a manner as to surround the cross-section of the core (i.e., in such a manner as to link up with the annular core in the form of a chain), resulting in a short-circuit current flowing. Thus, there is an energy loss due to the resistance component of the short-circuit, which results in a reduction in the energy generated in the secondary winding of the ignition coil. In addition, part of the energy thus lost is consumed in the heat dissipating plate, thus causing an additional rise in temperature.